This invention relates to the manufacture of cups, and more particularly to nestable cups made from compressed, foam sheet plastic. Disposable, foam sheet plastic cups have gained a substantial portion of the market which formerly used only cups made of paper. The greatest inroads made in this market by foamed plastic cups have been in the line of hot drink cups.
It is well known in foam plastics art that good thermal insulation may be obtained by providing the foam plastic cup with thick walls, but thick walls cause a corresponding increase in the nesting height of a stack of such cups. It is essential that nesting height be small to achieve low shipping costs and large capacity per unit volume in equipment such as vending machines where such cups might be used.
Most hot drink cups are manufactured by a bead molding process. The problem with this type of cup is that, due to expansion of the beads prior to molding, the cup cannot be made thin enough for many applications, such as vending machines. Thus, a second method of manufacturing hot drink cups was devised (see U.S. Pat. Nos. 3,069,725 and 3,312,383) wherein one or two pieces of foam sheet are molded to form a cup. However, the foam sheet molding methods present the problem of cracking when it is desired to form small diameter frustrums of cones. The blanked, arcuate sidewall must be wrapped around a small diameter, cup-shaped male mold or inserted into a female cavity prior to the molding operation and the presence of a substantial skin (a layer of very high density foam, approaching the density of the solid plastic itself) on the inner surface or both surfaces of the foam sheet is likely to result in cracks or corrugations, which will not be corrected in the subsequent molding operation.
The instant invention solves the problems outlined above by providing a disposable, plastic foam, heat sealed cup characterized by a unique cell size arrangement and surface characteristics.